Trauma, and hemorrhage suppress T-cell function through anti-inflammatory mediators. Suppressed T-cell function is considered to be in part responsible for the high incidence of post-traumatic sepsis which is the leading causes of all late trauma deaths in the USA. In recent years, hypertonic saline (HTS) resuscitation of trauma patients has been shown to reduce post-operative complications and mortality. Our preliminary studies have shown that HTS at clinically relevant levels enhances immune function in vitro and in vivo, and abrogates immunosuppression after hemorrhage resulting in significantly increased survival after experimental sepsis. However, the mechanisms leading to these improvements are not known. Recent reports have shown that HTS directly activates cellular signaling events (stress activated MAP kinases p38 and JNKs) in bacteria, yeast, and certain mammalian cells. In addition, osmosensing receptors that can activate these MAP kinases were found in yeast. These findings are the basis of our working hypothesis: T-cells may also have osmosensors through which HTS may cause MAP kinase activation. These MAP kinases may provide an additional activation signal that enhances proliferation of normal T-cells. In suppressed T-cells of trauma patients, the HTS activated signaling pathway may restore T-cell function by bypassing signaling pathways that are blocked via the action of trauma-induced anti-inflammatory factors. This may reverse trauma/hemorrhage induced immunosuppression, restore normal immune function and reduce the risk of post-traumatic sepsis and death. The following questions are investigated to test this hypothesis: i) What are the signaling pathways of HTS in T-cells? This part is designed to study the effects of HTS on early and late signaling events. Particular emphasis will be placed on the activation of MAP kinase cascades (particularly p38 and JNKs) and the upstream signaling events including protein tyrosine kinases (PTKs), phospholipase Cg1 (PLCgamma1), protein kinase C (PKC). In addition, the effect of HTS on late activation events (T-cell cycle progression) will be studied by measuring transcription and expression of IL-2 and IL-2R, as well as proliferation. 2) Can HTS restore suppressed T-cell function? This part is designed to study the effect of HTS on signal transduction in suppressed T-cells. Suppressed T-cells are obtained from trauma patients and through exposure of normal T-cells to serum factors from trauma patients or to anti- inflammatory mediators (PGE2, IL-4, IL-10, TGFBeta). The studies outlined in this proposal are important to understand when and how HTS influences normal and suppressed T-cell function. This will allow to judge and optimize the efficacy of HTS resuscitation to restore cellular immune function following trauma which may reduce lethal post- traumatic sepsis.